Thats a screaming good deal. Local too. A 74 duster is still an A body like yours His upper control arms are the big ball joint ones. Thats what you use with those disc spindles with no adaptorr sleeves. You will need a ball joint for the one upper control arm thats painted. Its a K772 joint. As well as bushings for it. Might as well rebuild both of them with new joints and bushings if your going to use them. Or you can use the small ball joint ones on your car with the adaptor sleeves
The lower control arms are the same part from 1962 to 1976. Only difference is some have tabs welded on them for swaybars. The ones on your car will work for this swap.
You will need the A body disc brake hoses from 74 to 76, disc brake proportioning valve for A body from 74 to 76, and the manual brake A body disc brake master cylinder from 74 to 76.
If you decide to use your small joint arms with the adaptor sleeves, and original lower control arms, you can sell the big joint arms, and those nice painted lower control arms and recoup some of your money. Id look on fabo sales and see what the going rate is on those pieces before selling them.
The bonus is the big bolt pattern wheels. You will notice the disc brakes come with way bigger studs 1/2" instead on the 7/16" ones on your drums.